#include<iostream>
using namespace std;
class Solution {
public:
    char firstUniqChar(const string& s) {
        char str[26] = { '\0' };
        for (const auto& ch : s)
            str[ch - 'a']++;
        char retch = ' ';
        for (const auto& ch : s)
        {
            if (str[ch - 'a'] == 1)
            {
                retch = ch;
                break;
            }
        }
        return retch;
    }
};
int main()
{
    string str;
    cin >> str;
    cout << Solution().firstUniqChar(str) << endl;
	return 0;
}